Process of separating gold from silver and other metals.



UNITE STATES PATENT FFIGE.

PROCESS OF SEPARATING GOLD FROM SILVER AND OTHER METALS.

Specification of Letters Patent.

Patented March 5, 1907.

Application filed February 23, 1905. Serial No. 247,017.

To all whom it may concern:

Be it known that I, DONALD CLARK, a subject of the King of Great Britainand Ireland, and a resident of Bairnsdale, in the State of Victoria,Commonwealth of Australia, have invented a certain new and usefulimprovement in the process for the separation of gold from silver andother metals and metallic substances with which it is commonlyassociated in slimes and in precipitates on zinc or other metals orsubstances, of which the following is a specification.

This invention relates to an improved process for the separation of goldfrom silver and other metals and metallic substances with which it iscommonly associated in slimes and in precipitates on Zinc or othermetals or substances.

The slimes or precipitates which I treat by my process are those whichin addition to gold contain silver or silver and other metals ormetallic substances such as alloys, compounds, and salts -and by myprocess the silver (no matter what proportion is present) or the silverand base metals are separated from the gold prior to smelting or amalgamation, and I am enabled to recover the silver in a solution containinglittle or no free acid and to leave the gold in such a state that it maybe readily washed,fluxed off, or a'malgamated.

In carrying out my process I take the slimes or precipitates such as areabove referred to and remove calcium carbonate or calcium hydroxid (orother salts of calcium,) if such be present, by means of dilutehydrochloric acid, the calcium chlorid so formed being removed bydecantation or filtration. Should no soluble calcium compounds bepresent, this preliminary treatment is not necessary, and even when suchcompounds are present and such preliminary treatment is not resorted tothey only interfere in subse quent operations by increasing the bulk ofthe insoluble salts present with the gold. After such treatment withdilute hydrochloric acid or without such treatment, if it beomitted, itis well, especially if the slimes or precipitates arenot free fromcoarse me tallic fragments and there are present metals, such as zinc,readily attacked by sulfuric acid, to treat the slimes or precipitateswith dilute sulfuric acid, whereby the compounds formed of the metalsreferred to may be removed by washing with Water, the liq- ,uorcontaining the soluble sulfates being removed by filtration ordecantation, or by both processes. These preliminary treatments arealready known and adopted, and I make no special claim therefor exceptin con junction with the process hereinafter described; but I may addthat in many processes it is the aim to entirely remove the solublesulfates before smelting, while in my process this isnot essential, andin some cases the preliminary treatment is not necessary at all, owingto the substances affected not being present in large quantities or particles. The residual slimes or precipitates, or if these prclin'iinaryoperations are dispensed with the original slimes or precipitates, areplaced in avessel of porcelain, castiron, or other substance notaffected by the substances hereinafter referred to and a solution of anysalt of the alkalies and sulfuric acid or a sulfate of the alkalies orsulfuric acid alone added and the mixture evapora ted to dryness andthen heated so as to cake the mass, and so prevent loss by dusting, alsoto form sulfates with some of the base metals present and to preventexcessive frothing in subsequent operations. Pyrosulfate of sodium isthen mixed in the same or similar vessel with the caked product and thewhole mixture heated. Instead of pyrosulfate of sodium I find that nitercake or bisulfates or disulIates of the alkalies or sulfuric acid orammonium sulfate and any salt or compound of the alkalies resulting inthe formation of a pyrosulfate or his ulfate will also bring about thedesired result.

The amount of pyrosulfate or of niter cake or other such substance to beadded will depend on the quantity of base metals and silver present; butin all cases enough must be added to transform these to sulfates. Thismay be done by adding a slight excess of the material or by regeneratingthe sodium sulfate which forms with sulfuric acid. The proper amount touse will vary with the different materials to be treated and can easilybe ascertained by a few trials. The temperature required lies above thatat which sulfuric acid is volatilized, but below that at which thesulfates of the base metals are decomposed in the presence of thepyrosulfate or other such substance. If the mixture is overheated andsulfates are decomposed, then this excessive heating may be corrected byadding more bisulfate or some strong sulfuric acid, when the sulfateswill be regenerated. Even where silver sulfate is decomposed, and insome cases it may be desirable to so raise the temperature, the metalsmay be separated by a method hereafter described.

After fusion the fused product is removed and the soluble salts removedby a water wash. If a small amount of silver is pres ent, it may bewholly removed. by washing it out with hot water. If larger quantitiesare present or the silver sulfate has been de composed by the heat, thesilver can be removed by heating the mass with strong sulfuric acidafter the soluble salts of the alkalies and other salts are removed. Thesilver sulfate readily dissolves, and the clear solution may be pouredoff and the silver recovered from this by well-known means. The smallamount of silver sulfate still remaining with the gold may be washed outwith hot water. The silver in all these solutions may be recovered fromthese solutions in a form from which pure silver may be prepared bywell-known means. The insoluble material left after the silver has beenwashed out may and probably will now, in addition to gold, consist ofsilicious gangue and insoluble sulfates, such as lead sulfate andcalcium sulfate, if the latter had. not been removed by the preliminaryoperation before described. Both lead and calcium sulfates may beremoved by first digesting the insoluble material in a hot solution ofsodium carbonate until the solution remains alkaline, then washing withwater until the solution becomes neutral, then treating the insolublematerial with nitric or acetic acid until effervescence ceases, and thenwashing out the salts of lead and calcium with water. The insolublematerial would then only consist of gold and silicious material. may bereadily recovered in a pure state by fluXing off the silicious materialby smelting. Even when sulfates of lead and calcium and siliciousmaterial remains with the gold these may be all readily fluXed out andthe gold recovered by smelting.

I prefer instead of fluxing off or otherwise removing these insolublematerials to add mercury and amalgamate the gold present. The greaterportion of the gold is in a state which causes it to amalgamate veryreadily; but some very finely divided gold which is usually present ismore diflicult to amalgamate. In such cases I therefore add cyanid ofpotassium, which quickens the action and causes a very speedyamalgamation. Should any fine gold be dissolved during the operation bythe cyanid added, then this may be recovered by causing the solutioncontaining it to pass over zinc filaments. The gold will be precipitatedin a pure state. After The gold amalgamation has taken place and thecyanid solution washed out the amalgam may be collected from theinsoluble material by well-known means and the gold recovered byretorting. The retorted gold may be smelted, when it will be found to bepractically pure.

Having now described my invention, what I claim as new, and desire tosecure by Letters Patent, is

1. The process herein described of separating gold from silver and othermetals and metallic substances with which it is commonly associated inresiduum slimes recovered from prior treatment of crude ores or metalswhich consists: first, in subjecting such slimes to the action of dilutehydrochloric ac1d until the compounds of calcium readily soluble in suchacid are dissolved and removing the same by a water wash; secondly,subjecting such slimes to the action of dilute sulfuric acid until thecoarse particles if any of the metals soluble in dilute sulfuric acidare dissolved and in removing the clear liquid containing the sulfatebut not necessarily washing them all out thirdly, drying such slimeswith the addition of sulfuric acid and a soluble sulfate and heating thecaked product; fourthly, applying to the caked product a pyrosulfate ofthe alkalies and heating until the base metals and silver aretransformed to sulfates; fifthly, subjecting the fused mass to a waterwash to remove sodium salts and the silver if in small pro portions, orthe silver sulfate has been decomposed by heat; siXthly, removing silversulfates if present in large quantities by means of sulfuric acid thatthe gold may be readily removed and collected by amalgamation.

2. In the rocess herein described of separating gold f fom silver andother metals and metallic substances with which it is commonlyassociated in residuum slimes recovered from prior treatment of crudeores which consists in subjecting said residuum slimes to the action ofsulfuric acid and a soluble sulfate and heating the product so as tocake the same and afterward subjecting the product to the action ofniter cake and heating the same so as to form sulfates of the basemetals and silver, afterward washing out such sulfates leaving thesilver and insoluble gold readily recoverable substantially ashereinbefore described.

In witness whereof I have hereunto set my hand in presence of twowitnesses.

DONALD CLARK.

Witnesses:

LESLIE LAWTON BEAR, HERMAN IIUGO BRIESE.

